1. Field of the Invention
The present invention relates to a knee brace and is directed more specifically to the provision of a patella support brace which is characterized in that a progressively increasing medially directed force is applied against the patella as the leg of the wearer shifts from a flexed to an extended condition.
2. The Prior Art
The patella of the knee joint rides in the femoral trochlea which is in the nature of a valley extending laterally of the joint. Secured to the patella and maintaining the same in its disposition within the trochlea is the upwardly directed patella ligament and downwardly directed tendons extending from the quadriceps muscles. The force angle of the quadriceps and patella tendons intersect and act on the patella at an obtuse and laterally outwardly directed angle known as the Q angle.
Due to the angular relationship of the forces exerted on the patella when the knee joint is shifted from the condition of flexion to a condition of extension, a laterally directed force vector, known as the valgus vector, is exerted against the patella. The valgus vector tends bodily to shift the patella outwardly progressively as the knee joint is straightened. Additionally, as the leg is straightened, a rotary movement is imparted to the lower leg components, functioning to increase the Q angle.
The femoral trochlea becomes progressively shallower in the area occupied by the patella as the knee joint approaches a condition of extension, and thus the constraining influence of the trochlea on the patella is progressively reduced as the leg approaches a fully extended condition.
The net effect of the various conditions above described, namely, valgus vector forces, rotation of the tibia during extension, and progressive depth reduction of the femoral trochlea, often lead, especially during violent activity, to a condition in which the patella subluxes or moves undesirably in a laterally outward direction relative to the femoral trochlea.
The subluxing forces exerted on the patella are often exacerbated by other stresses to which the knee joint is subjected in the course of physical activity.
Numerous attemps have been made to design knee braces which will prevent patella subluxation while at the same time avoiding discomfort to the wearer. No device hereotofore known has been entirely successful in accomplishing both of the noted results.
Numerous knee braces have been designed which include apertures intended to surround the patella and fix the patella against undue lateral outward movement. Alternative arrangements including cumbersome straps, bands and splints have been proposed, the objective in each instance being to confine the patella.
By way of example of braces appearing in the patent literature reference is made to the following patents: U.S. Pat. Nos. 1,388,772 of Aug. 23, 1921; 2,220,836 of Nov. 5, 1940; 2,270,685 of Jan. 20, 1942; 3,046,981 of July 31, 1962; 2,804,084 of Apr. 16, 1974; 3,945,046 of Mar. 23, 1976; 4,084,584 of Apr. 18, 1978; 4,116,236 of Sept. 26, 1978; French Patent No. 840,438 of Jan. 16, 1939, and British Patent No. 160,032 of 1898.
All of the above noted references represent examples of braces, sleeves or bands intended to minimize the likelihood of patella subluxation by the surrounding of or confinement of the patella, or restraint of the knee.
A slightly different approach to the problem is embodied in U.S. Pat. No. 4,296,744 of Oct. 27, 1981. In accordance with this patent, a patella pad is retained against the outer lateral surface of the patella. Elastic bands are secured to the patella pad in such manner that a resilient, medially directed force is exerted against the patella pad continuously throughout the range of movement of the knee joint.
The structure of the noted reference involves several major shortcomings. Specifically, since the force applied against the patella pad and, hence, against the patella, is continuously exerted, i.e. in condition of flexure where no restraining force is needed as well as at a condition of extension where it is required, the knee joint is subjected needlessly to a continuous compressive influence. Secondly, due to the geometry of the appliance, movement of the knee from the flexed to the extended condition actually reduces the force exerted against the patella progressively as the knee approaches a condition of extension Additionally, since the forces are continuously exerted, it is possible to apply relatively limited medially directed forces to avoid constriction and strangulation of the knee.
Thus the device acts in an exactly opposite way to an ideal condition wherein minimal forces are exerted when the knee is flexed, and the forces progressively increase as the knee approaches extension, the position at which the danger of subluxation is at its greatest. Summary of the Invention
The present invention may be summarized as directed to a knee brace or patella splint wherein little or no medially directed forces are exerted against the patella when the knee is in flexed condition, the force progressively increasing as the leg approaches a condition of extension.
More particularly, the present invention is directed to a patella support device which relies on the straightening of the leg to produce kinetic forces of progressively increasing magnitude which are exerted against a patella pad increasingly to urge the patella pad in a medial direction against the lateral surface of the patella, thereby to reduce the possibility of subluxation of the patella.
Since the forces exerted against the patella during the initial ranges of movement, i.e. when the leg is in a fully flexed or a partially straightened condition, are low, there is little discomfort to the wearer as the patella is not forced bodily into the femoral trochlea. Where the leg approaches its condition of full extension, a very significant medial and/or combined medial and downward force is exerted against the patella.
It is accordingly an object of the invention to provide an improved knee splint or brace characterized in that a progressively increasing medial force is exerted on the patella responsive to movements of the leg to the flexed or straightened condition.
A further object of the invention is the provision of a device of the type described wherein the force noted is developed responsive to straightening of the leg whereby the force is automatically reduced when the leg is flexed and exerted at progressively increasing values as the leg approaches the extended condition.